Nature of the phase transitions in [(C2H5)4N]2MCl4 complexes (M = cobalt, copper)

Single-crystal ESR spectra of undiluted [(C2HJ4NI2MCl4(M = Co, Cu) are reported. The spectra of the cobalt complex are quite similar to those of the zinc-doped complex. The spectra of the copper complex are temperature dependent, giving gI1 =-2.29 and g, = 2.16 at room temperature, gl = 2.10 and g, = 2.29 at intermediate temperature, and gll = 2.46 and g, - 2.10 at 4.2 K. This behavior is interpreted as due to dynamic distortions of the pseudotetrahedral chromophores between two equivalent compressions. A similar behavior is suggested also for the cobalt complex.